1. The Field of the Invention
The present invention relates generally to magnesium hydroxide nanoparticles, methods of making magnesium hydroxide nanoparticles, and compositions incorporating such nanoparticles. Magnesium hydroxide nanoparticles are made using an organic agent having at least two functional groups that influence the size, shape and/or dispersibility of the nanoparticles.
2. The Relevant Technology
Fires are a frequent and dangerous hazard throughout the world. Every year fires kill people and cause substantial economic loss. According to statistics, the monetary loss due to fire is equivalent to 0.2% to 0.3% of the GNP of European and North American countries. Despite extensive fire prevention measures and fire fighting efforts, there are thousands of fire-related deaths in all countries, including developed countries in Europe and North America.
Many materials can be made less hazardous in a fire by including a flame retardant. Flame retardants are often used as filler materials in plastics and other materials for their ability to inhibit combustion and smoke generation.
There are many classes of compounds that are useful as flame retardants. Inorganic minerals, organo-phosphates, and halogenated compounds are commonly used in plastics and other materials. Magnesium hydroxide is a known flame retardant that is attracting substantial attention because of its performance, price, low corrosiveness, and low toxicity. The current market for magnesium hydroxide in flame retardants is about ten million pounds per year.
Magnesium hydroxide (Mg(OH)2) is an acid-free, halogen-free flame retardant suitable for use in plastics. Both hydroxide ions in magnesium hydroxide decompose endothermically when heated to temperatures greater than 340° C. The decomposition of Mg(OH)2 has the following formula: Mg(OH)2→MgO+H2O 1316 J/g.
The high decomposition temperature of magnesium hydroxide results in the absorption of larger amounts of heat energy than other known flame retardants. For example, aluminum trihydroxide (ATH) decomposes at 200° C. according to the following formula. 2Al(OH)3→Al2O3+3H2O 1051 J/g. As can be seen from the equations, the decomposition of magnesium hydroxide consumes 265 J/g more heat energy than ATH. In addition, the 100° C. higher decomposition temperature of magnesium hydroxide (compared to ATH) allows magnesium hydroxide to be processed in plastics at higher temperatures.
The decomposition products of manganese hydroxide (i.e., water and MgO) are non-toxic, and the mineral phase, MgO, is alkaline, which reduces the likelihood that acidic, corrosive gases will be formed and/or escape from the plastic when heated to combustion temperatures.
The gaseous water formed in the decomposition of the magnesium hydroxide is believed to envelop the flame, thereby excluding oxygen and diluting flammable gases. Similar to the function of char formed by phosphorous-containing flame retardants, a heat insulating material comprising MgO may form on the surface of the plastic in contact with the flame, reducing the flow of potentially flammable decomposition products to the gas phase where combustion occurs.
Magnesium hydroxide is typically incorporated into plastic as a finely divided powdery filler. To obtain the desired fire retarding properties, the magnesium hydroxide is added to plastics in relatively high amounts. In some cases, the weight of the magnesium hydroxide filler is equal to the weight of the plastic material. Including large amounts of a particulate filler, however, can have a negative effect on the tensile strength and other mechanical properties of the plastic material. Plastic materials having large quantities of magnesium hydroxide have also been known to absorb water, thereby decreasing tensile strength and increasing the rate of aging.